Field of the Invention
This invention relates to systems and methods for maintaining intelligent write ordering in asynchronous data replication environments.
Background of the Invention
Storage systems such as the IBM DS8000™ enterprise storage system may utilize a cache algorithm known as Intelligent Write Caching (IWC). This algorithm may improve performance by better managing the write cache and improving the order in which writes are destaged from the write cache to spinning disk drives. In general, this algorithm may reduce seek and rotational penalties for spinning disk drives and also improve RAID parity generation by allowing some parity operations to be performed as a group.
Unfortunately, performance improvements of Intelligent Write Caching may be lost or impaired when asynchronously mirroring data between storage systems, particularly with certain types of workloads. For example, certain types of workloads in asynchronous data replication systems may alter the order in which writes are destaged from the write cache using Intelligent Write Caching. This can impair performance by increasing the amount or percentage of time spent seeking for write locations on the disk drives.
For example, when mirroring data from a primary storage device to a secondary storage device in an asynchronous data replication system, writes may be stored in the write cache of the secondary storage device. This can cause problems where previous versions of data that are being overwritten belong to a previous consistency group. In such cases, the previous versions of the data in the secondary write cache may need to be preserved prior to writing the new data. This causes the prior version of the data be destaged from the secondary write cache prior to writing the new data, thereby altering the order that data would normally be destaged from the secondary write cache using the Intelligent Write Caching algorithm. As mentioned above, this can impair performance by increasing the amount or percentage of time spent seeking for write locations on spinning disk drives.
In view of the foregoing, what are needed are systems and methods to maintain intelligent write ordering in asynchronous data replication environments. Ideally, such systems and methods will improve the order in which writes are destaged to disk from the secondary write cache.